(1) Field of the Invention
This invention relates to a rolled steel having excellent resistance to sulfide stress corrosion cracking and a process for producing same.
(2) Description of the Prior Art
While a rolled steel is used under stress loads in a wet H.sub.2 S environment, hydrogen which has been formed due to progress of corrosion reactions penetrates into the steel and accumulates at a location where stresses are centralized. Due to its synergistic effect with stresses, a type of hydrogen embrittlement takes place. This phenomenon is generally called sulfide stress corrosion cracking.
As countermeasures against the above-mentioned sulfide stress corrosion cracking, it has conventionally been recommended to use steels having hardnesses lower than a certain level or to completely temper steels into tempered martensite structures because the sulfide stress corrosion cracking susceptibility of steels is heavily dependent on the strengths (i.e., hardnesses) of the steels. Additionally, it has also been attempted to reduce the segregation of impurity elements, e.g., P or to lower the contents of relative large impurities.